JP3203745B2 - Fluorine-containing water treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating fluorine-containing water, and more particularly, to a system for discharging low-concentration fluorine-containing water and high-concentration fluorine-containing water, whereby each fluorine-containing water can be efficiently produced at low cost. And a method for efficiently recovering fluorine.

[0002]

2. Description of the Related Art In the field of semiconductor manufacturing and related fields, and in the field of surface treatment of various metallic materials, single crystal materials, optical materials, and the like, a large amount of an etching agent is used. As the etching agent, an etching agent mainly containing hydrogen fluoride or hydrogen fluoride and ammonium fluoride is mainly used.

An etching agent containing hydrogen fluoride as a main component is an etching agent containing about 0.9% of fluorine as HF, and is used in a large amount. On the other hand, the etchant (buffered hydrofluoric acid) containing hydrogen fluoride and ammonium fluoride, although used in a small amount, contains about 7% of fluorine as HF, which is a problem when transferred to a wastewater system. . That is, these etching agents flow out to the wastewater system as they are, and become a high-concentration fluorine-containing wastewater.

On the other hand, during the etching or at the end of the etching, the material treated with the etching agent is washed with a large amount of washing water, and a large amount of low-concentration fluorine-containing waste liquid is discharged from the washing step.

Heretofore, these high-concentration fluorine-containing waste liquids and low-concentration fluorine-containing waste liquids have been mixed and treated collectively. For the treatment of this fluorine-containing waste water, a method of adding a calcium salt such as calcium hydroxide (Ca (OH) ₂ ) to precipitate and remove it as calcium fluoride (CaF ₂ ) is generally used.

Alternatively, a high-concentration fluorine-containing waste liquid and a low-concentration fluorine-containing waste liquid are separated, and the high-concentration fluorine-containing waste liquid is subjected to precipitation treatment with a calcium salt, and the treated water obtained (fluorine concentration: about 200 mg-HF / liter) Is mixed with a low-concentration fluorine-containing waste liquid, and a calcium salt or an aluminum salt is added together with the calcium salt in a wastewater treatment facility to carry out coagulation sedimentation treatment. In this case, the final effluent has a fluorine concentration of 8 mg-HF / liter or less, and the precipitate is treated as waste sludge.

[0007]

Among the above-mentioned conventional methods, a method of mixing high-concentration fluorine-containing waste liquid and low-concentration fluorine-containing waste liquid to collectively treat the fluorine to a value equal to or lower than the wastewater standard value is required. A large excess of calcium salt needs to be added. In addition, it is extremely difficult to efficiently treat in a short time only by adding the calcium salt.

Further, in the method of separating the high-concentration fluorine-containing waste liquid and the low-concentration fluorine-containing waste liquid, a large amount of waste sludge is generated in the final coagulation and sedimentation treatment, and there is a problem in sludge treatment.

By applying a fluorine-adsorbing resin to this coagulation-sedimentation treatment system, it is possible to maintain the quality of treated water stably and to reduce the amount of sludge generated. In this case, the fluorine concentrated by the fluorine-adsorbing resin is usually returned to the raw wastewater tank, treated again, and finally discharged out of the system as waste sludge.

At present, there is a system for producing hydrofluoric acid (HF) again from the fluorine contained in the high-concentration fluorine-containing waste liquid and the low-concentration fluorine-containing waste liquid recovered as CaF _{2 with} calcium carbonate (CaCO ₃ ). It has been studied, and it has been desired to efficiently recover the fluorine removed from the high-concentration fluorine-containing waste liquid and the low-concentration fluorine-containing waste liquid without discharging it as waste sludge.

The present invention solves the above-mentioned conventional problems, and in a system in which low-concentration fluorine-containing wastewater and high-concentration fluorine-containing wastewater are discharged, these fluorine-containing wastewaters can be efficiently treated in a short time at low cost. An object is to provide a method for obtaining high-purity treated water and efficiently recovering fluorine.

[0012]

The method for treating fluorine-containing water according to the present invention is directed to a method for treating fluorine-containing water using a calcium compound and a fluorine-adsorbing resin. Separating fluorine-containing water and high-concentration fluorine-containing water, adding a calcium compound to low-concentration fluorine-containing water, performing solid-liquid separation, contacting the separated liquid with a fluorine-adsorbing resin, regenerating the fluorine-adsorbing resin, And adding a regenerated waste liquid of the fluorine-adsorbing resin to the high-concentration fluorine-containing water and passing the solution through a calcium carbonate crystal seed filling tank.

The present invention will be described below in detail with reference to the drawings. FIG. 1 is a system diagram showing one embodiment of the method for treating fluorine-containing water of the present invention.

In FIG. 1, 1, 5, 9, and 12 are storage tanks, 2 is a mixing tank, 3 is a coagulation tank, 4 is a sedimentation tank, 6 is a sand filtration tank, 7 is a fluorine adsorption resin tower, and 8 is pH adjustment. The tank, 10 is a concentration tank, 11 is a dehydrator, and 13 is a CaCO ₃ filling tank.

Reference numeral 20 denotes a pipe for introducing the low-concentration fluorine-containing waste liquid into the storage tank 1, reference numeral 21 denotes a pipe for supplying the water stored in the storage tank 1 to the mixing tank 2, and reference numeral 22 denotes a sand filtration tank for storing the water stored in the storage tank 5. 6, a pipe for supplying the filtrate of the sand filtration tank 6 to the fluorine adsorption resin tower 7, a pipe 24 for supplying the treated water of the fluorine adsorption resin tower 7 to the pH adjustment tank 8, and a pipe 25. This is a discharge pipe for treated water in this treatment step. 26 is a pipe for feeding the sediment in the sedimentation tank 4 to the concentration tank 10, 27 is a pipe for feeding the concentrate in the concentration tank 10 to the dehydrator 11, 28 is a discharge pipe for the dehydrated cake, and 29 is a pipe for dehydrator 11. This is a pipe for returning the separated water to the storage tank 1. 30 is a storage tank for storing a high-concentration fluorine-containing waste liquid.
2 is a pipe for feeding the water stored in the storage tank 12 to Ca.
A pipe for feeding the CO ₃ -filled tank 13, a pipe 32 for extracting CaF _2, a pipe 33 for feeding the treated water of the CaCO ₃ -filled tank 13 to the storage tank 1, and a pipe 34 for recycling the waste liquid from the fluorine adsorption resin tower 7 It is a discharge pipe, and is branched into a pipe 34A for supplying the concentrated regeneration waste liquid to the storage tank 12 and a pipe 34B for supplying the non-rich regeneration waste liquid to the storage tank 1. 35 is a calcium compound supply pipe, 36 is a coagulant supply pipe, 37 is HC
1 is a supply pipe, and 38 is a NaOH supply pipe.

In the present invention, the high-concentration fluorine-containing water and the low-concentration fluorine-containing water are separated without mixing.

Here, the high-concentration fluorine-containing water and the low-concentration fluorine-containing water include, for example, the treatment process wastewater using the above-mentioned etching agent and the washing wastewater. The standard of high-concentration fluorine-containing water is 500 mg-HF /
The standard for wastewater over 1 liter and low-concentration fluorine-containing water is 5
Wastewater of less than 00 mg-HF / liter.

In the illustrated embodiment, low-concentration fluorine-containing wastewater is mixed with separated water from a dehydrator 11 and non-concentrated regenerated wastewater from a fluorine-absorbing resin tower 7 through a pipe 20, a storage tank 1, and a pipe 21. It is fed to the tank 2 and a calcium compound such as Ca (OH) ₂ is added. In addition, the etching agent-containing wastewater, which is one of the preferable treatment target waters of the present invention, includes:
In many cases, hydrogen peroxide is included. Since hydrogen peroxide not only inhibits precipitation and separation but also deteriorates the subsequent resin, it is preferable to decompose hydrogen peroxide by using a reducing agent such as NaHSO ₃ or a hydrogen peroxide decomposing enzyme in combination. In addition, an inorganic acid such as H ₂ SO ₄ or HCl is added and mixed as a pH adjuster.

The liquid mixture in the mixing tank 2 is subjected to coagulation treatment by adding a coagulant such as polyacrylamide partial hydrolyzate in the coagulation tank 3 and then settled and separated in the settling tank 4, and the sediment (sludge) is piped. From 26, the supernatant water is fed to the concentration tank 10, while the supernatant water is transferred to the storage tank 1.

Here, as a calcium compound to be added to the mixing tank 2, calcium chloride (CaCl ₂ ) is used in addition to basic calcium compounds such as calcium oxide (CaO) and calcium hydroxide (Ca (OH) ₂ ). It is preferable that the amount of addition be about 0.5 to 3 equivalents of fluorine ions in the water to be treated in terms of Ca. It is preferable to appropriately adjust the pH in the mixing tank 2 to be about 6 to 11. The amount of the coagulant added to the coagulation tank 3 is preferably about 0.01 to 10 ppm.

The reaction conditions in the mixing tank 2 and the coagulation tank 3 are not particularly limited, but usually, the residence time is 1 minute to 5 minutes.
In about an hour, it is treated under rapid stirring.

From the sedimentation tank 4 through the pipe 26, the concentration tank 10
Is concentrated here, and then sent to the dehydrator 11 via the pipe 27 to be subjected to dehydration treatment. The dehydrated cake is discharged out of the system through a pipe 28, and the separated water is returned to the storage tank 1 through a pipe 29, and is treated together with the low-concentration fluorine-containing waste liquid.

On the other hand, the water stored in the storage tank 5 is sent to the sand filtration tank 6 via the pipe 22 and is subjected to sand filtration. The filtrate is adjusted to pH 3 with an acid such as HCl from a pipe 37 in a pipe 23.
After being adjusted to about 7, it is fed to the fluorine-adsorbing resin tower 7 and is brought into contact with the fluorine-adsorbing resin to be adsorbed. Thereby, the coagulated and separated water such as the low-concentration fluorine-containing waste liquid is easily treated to a discharge water standard value (15 mg-HF / liter) or less because of its low fluorine content.
The treated water obtained by the adsorption treatment in the fluorine adsorption resin tower 7 is sent from the pipe 24 to the pH adjusting tank 8, and the pH is adjusted by adding an alkali such as NaOH as necessary from the pipe 38, and then stored in the storage tank. 9. Discharged out of the system via the pipe 25. The resulting treated water is below the effluent standard value,
It may be discharged as it is, or it may be recovered and reused as raw water for producing ultrapure water or other industrial water.

As the fluorine-adsorbing resin, for example,
Examples thereof include a resin adsorbing a metal ion that forms a complex compound with fluorine ions such as cerium, hafnium, titanium, zirconium, iron, aluminum, and lanthanide, activated carbon, activated alumina, hydrous titanium oxide, zeolite, and a magnesia-based adsorbent. In addition, the conditions for the adsorption treatment are not particularly limited, but the treatment is performed, for example, at an SV of about 0.5 to 30 hr ^-1 .

The fluorine adsorption resin tower 7 stops the adsorption treatment and supplies a regenerant to perform the regeneration treatment, if necessary. As the regenerant, an aqueous solution of sodium hydroxide, potassium hydroxide, hydrochloric acid, sodium carbonate or the like is used. Since a part of the regenerated waste liquid obtained by the regenerating process contains a large amount of fluorine components, it is fed to a high-concentration fluorine-containing waste liquid storage tank 12 described below via pipes 34 and 34A for processing.

By the way, the fluorine concentration of the regenerated waste liquid obtained by the regenerating process changes with time. That is, in the very early stage of the regeneration, a regeneration waste liquid containing almost no fluorine flows out, and in the early to middle stages of the regeneration, a concentrated regeneration waste liquid containing a relatively high concentration of fluorine flows out. The fluorine concentration in the waste liquid decreases.

In this embodiment, only the concentrated regenerated waste liquid having a high fluorine content, which flows out from the initial to the middle stages of the regeneration, is fed to the storage tank 12, and the very early and late stages of the regeneration are performed. The non-concentrated regenerated waste liquid having a relatively low fluorine content flowing out to the storage tank 1 is supplied to the storage tank 1 via the pipes 34 and 34B, and is treated with the low-concentration fluorine-containing waste liquid.

As described above, by separating and treating the regenerated waste liquid into a concentrated regenerated waste liquid and a non-concentrated regenerated waste liquid, the load can be reduced and the fluorine recovery efficiency can be improved.

As a method of separating the regenerated waste liquid into a concentrated regenerated waste liquid and a non-concentrated regenerated waste liquid, for example, a timer is used to detect the pH of the regenerated waste liquid flowing out of the fluorine adsorption resin tower 7 or to detect the concentration of fluorine ions. It is sufficient to take out only the regenerated waste liquid having a detection value equal to or more than the detected value as the concentrated regenerated waste liquid for a predetermined time. Specifically, (i) a regeneration waste liquid having a pH in the range of 4-13.6 is collected for a predetermined time by setting a timer. (ii) Fluoride ion concentration of 1 using a fluoride ion selective electrode
A regenerated waste liquid of 00 mg-HF / liter or more is collected for a predetermined time by setting a timer. Such a method can be adopted.

On the other hand, the high-concentration fluorine-containing waste liquid is
The wastewater is further supplied to the storage tank 12 and introduced into the CaCO ₃ filling tank 13 via the pipe 31 together with the concentrated regenerated waste liquid from the pipe 34A for treatment. In the CaCO ₃ filling tank 13, most (about 98%) of fluorine in the liquid is recovered from the pipe 32 as CaF ₂ . This CaCO ₃ filling tank 1
The liquid from which fluorine has been removed in 3 is stored in a storage tank 1 through a pipe 33.
And treated with low-concentration fluorine-containing waste liquid.

Here, as the CaCO ₃ filling tank 13,
A material filled with CaCO ₃ crystal seeds having a particle size of about 0.1 to 0.5 mm is used, and the flow conditions are not particularly limited. For example, the treatment is performed at an SV of about 0.1 to 5 hr ⁻¹ .

According to the method of the present embodiment, the fluorine-containing water is separated into a low-concentration fluorine-containing waste liquid and a high-concentration fluorine-containing waste liquid, and the high-concentration fluorine-containing waste liquid and the concentrated regenerated waste liquid from the fluorine adsorption resin tower are converted into CaCO ₃ crystals. Seed treatment to convert fluorine to Ca
It can be efficiently recovered as F _2. After treating this fluorine-recovered treated water with a calcium compound together with a low-concentration fluorine-containing waste liquid and a non-concentrated regenerated waste liquid of a fluorine-adsorbing resin tower, by contacting with a fluorine-adsorbing resin, high-quality treated water is efficiently recovered. It is made possible.

The example shown in FIG. 1 is an embodiment of the method for treating fluorine-containing water of the present invention, and the present invention is not limited to the illustrated method. For example, in the method shown in the figure, the sedimentation tank 4 and the sand filtration tank 6 are used as solid-liquid separation means, but the present invention is not limited to this. For example, membrane separation using a reverse osmosis membrane, an ultrafiltration membrane, or a microfiltration membrane An apparatus may be used.

[0034]

According to the method for treating fluorine-containing water of the present invention,
Separation processing is performed without mixing low-concentration fluorine-containing water and high-concentration fluorine-containing water, and optimal processing can be performed according to each fluorine concentration. That is, the low-concentration fluorine-containing water can be easily converted into high-purity water having a discharge water standard value or less by the adsorption treatment. On the other hand, high-concentration fluorine-containing water can efficiently recover fluorine contained therein as CaF ₂ by reacting with CaCO ₃ together with the waste water of regenerating the fluorine-adsorbing resin. Since the recovered CaF ₂ is extremely high in purity,
It can be effectively reused as a raw material for producing hydrofluoric acid. Further, the treated water obtained by the adsorption treatment is extremely high in purity, and thus can be effectively reused as raw water for producing ultrapure water.

Moreover, the amount of sludge generated in the treatment of low-concentration fluorine-containing waste liquid is very small. Incidentally, according to the method of the present invention, the amount of generated sludge is 5 times less than that of the conventional method.
0-60% can be reduced, and operating costs can be reduced by 50-5
It can be reduced by about 5%. Further, by improving the processing efficiency, the installation area can be reduced by about 30%. Further, of the fluorine which has been conventionally subjected to wastewater treatment, 10 to 20
% As CaF ₂ and can be reused.

In particular, by separating the regenerated waste liquid into a concentrated regenerated waste liquid containing a high concentration of fluorine and a non-concentrated regenerated waste liquid and treating only the concentrated regenerated waste liquid together with a high-concentration fluorine-containing waste liquid, the load on the apparatus can be reduced and the CaF improvement of ₂ recovery efficiency can be achieved.

[0037]

The present invention will be described more specifically with reference to the following examples. In the following, the fluorine concentration is shown in terms of HF.

Example 1 A wastewater having a high concentration of fluorine and a wastewater having a low concentration of fluorine shown in Table 1 were treated according to the method shown in FIG. Each processing condition was as follows.

Mixing tank Ca (OH) ₂ addition amount: 750 ppm H ₂ SO ₄ addition amount: added until pH = 7 NaHSO ₃ addition amount: 650 ppm pH = 7 Residence time = 30 minutes Coagulation tank Coagulant (polyacrylamide part) Hydrolysate) Addition amount:
0.5 ppm Residence time = 5 minutes Fluorine adsorption resin tower Fluorine adsorption resin: resin kneaded with hydrated cerium oxide SV = 20 hr ^-1 pH = 3 CaCO ₃ filling tank CaCO ₃ particle size: 0.1 to 0.5 mm CaCO ₃ Filling amount: 1 liter SV = 1 hr ^-1 Effluent of the sand filtration tank 6 (Ca (OH) ₂ treated water) and effluent of the fluorine adsorption resin tower 7 (adsorption treated water) in the treatment system for low-concentration fluorine-containing waste liquid Table 1 shows the water quality.

[0040]

[Table 1]

The above-mentioned low-concentration fluorine-containing waste liquid is prepared for 500 to 60
0B. V. After the treatment, the fluorine adsorption resin tower was regenerated with 60 g-NaOH / liter-resin.
FIG. 2 shows the change over time in the water quality of the regenerated waste liquid in this regenerating process
As shown in FIG. Therefore, the effluent having a high fluorine concentration (the effluent having a pH of 4 to 13.6) indicated by the diagonal lines in FIG.
Separate for 0 minutes, and add CaCO
Treated in ₃ filling tanks.

As a result, 98% or more of the fluorine
It was able to be recovered by switching to ₂ . This recovered CaF ₂
The product CaF ₂ obtained from
Na ⁺ ions from H were not mixed. Note that C
The liquid obtained by the aF ₂ recovery treatment was again treated together with the low-concentration fluorine-containing waste liquid.

[0043]

As described above in detail, according to the method for treating fluorine-containing water of the present invention, in a system in which high-concentration fluorine-containing water and low-concentration fluorine-containing water are discharged, each fluorine-containing water is optimally treated. The method enables efficient and low-cost processing in a short time, and enables recovery of high-purity treated water and high-purity CaF ₂ . Moreover, the regeneration waste liquid from the adsorption tower can be treated at the same time, and the amount of sludge generated can be significantly reduced, which is industrially extremely advantageous.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a method for treating fluorine-containing water according to the present invention.

FIG. 2 is a graph showing the change over time in the water quality of the reclaimed waste liquid obtained in Example 1.

[Explanation of symbols]

1, 5, 9, 12 Storage tank 2 Mixing tank 3 Coagulation tank 4 Sedimentation tank 6 Sand filtration tank 7 Fluorine adsorption resin tower 8 pH adjustment tank 10 Concentration tank 11 Dehydrator 13 CaCO ₃ filling tank

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yukihiro Furukawa 3-4-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo Inside Kurita Kogyo Co., Ltd. (72) Inventor Naoto Ichiyanagi 3-4-2, Nishishinjuku, Shinjuku-ku, Tokyo No. Kurita Kogyo Co., Ltd. Inventor Matago Maeno 2-42-6 Komyodai, Izumi-shi, Osaka (56) References JP-A-5-92187 (JP, A) JP-A-3-118897 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C02F 1/58

Claims (1)

(57) [Claims] 1. A method for treating fluorine-containing water, wherein the fluorine-containing water is treated using a calcium compound and a fluorine-adsorbing resin, wherein the step of separating the fluorine-containing water into low-concentration fluorine-containing water and high-concentration fluorine-containing water. Adding a calcium compound to the high-concentration fluorine-containing water, performing solid-liquid separation, contacting the separated liquid with a fluorine-adsorbing resin, regenerating the fluorine-adsorbing resin, and reusing the regenerated waste liquid of the fluorine-adsorbing resin in high-concentration fluorine-containing water. After adding
A step of passing the solution through a calcium carbonate crystal seed filling tank.